We demonstrate that an offset stimulated emission depletion (STED) beam breaks the diffraction barrier of fluorescence microscopy in both the lateral and the axial directions. A 2.5-fold axial reduction of the focal spot is accomplished through the ear-shaped lobes of the diffraction maximum of the STED beam. The effect of the minima and side maxima of the STED beam on the lateral and axial resolution is shown to be in remarkable agreement with theory. Conditions are given for which a regular STED beam reduces the axial extent of a confocal spot from 490±36 to 175±18 nm, and simultaneously from 183±12 to 70±8 nm along the direction of the offset. The latter establishes the lowest reported value in far-field fluorescence microscopy.

High-temperature operation of a low-threshold 5.3 μm quantum-cascade distributed feedback laser is presented. The emission spectrum was single mode with more than 20 dB side mode suppression ratio for all investigated temperatures and up to thermal rollover. For 1.5% duty cycle and at the laser emitted 1.15 W of single mode peak power; at a value of 92 mW was seen. For a 3 mm long device, we observed a room-temperature threshold current density of This remarkable performance is mainly due to a 4 quantum-well active region using a double phonon resonance for the lower laser level.

Over 0.1 mW ultraviolet output was achieved by an AlGaN-based light-emitting diode. To realize a highly conductive and ultraviolet-transparent layer, a short-period alloy superlattice was introduced. The device was fabricated on SiC substrate. Low electric resistivity due to the short-period alloy superlattice and the high thermal conductivity of the SiC substrate enabled large current injection of up to The emission was monochromatic band-edge emission about 350 nm in wavelength without significant D–A and/or deep emissions.

We have investigated a SiGe/Si quantum-well laser based on transitions between the light-hole and heavy-hole subbands. The lasing occurs in the region of k space where the dispersion of ground-state light-hole subband is so nonparabolic that its effective mass is inverted. This kind of lasing mechanism makes total population inversion between the two subbands unnecessary. The laser structure can be electrically pumped through tunneling in a quantum cascade scheme. Optical gain as high as 172/cm at the wavelength of 50 μm can be achieved at the temperature of liquid nitrogen, even when the population of the upper laser subband is 15% less than that of the lower subband.

Bulk BeCdSe layer lattice-matched to a GaAs substrate, as well as a BeCdSe/ZnSe quantum well(QW)structure have been grown using the submonolayer digital alloying mode of molecular beam epitaxy. The structures have demonstrated bright photoluminescence up to room temperature and good structural quality. Stimulated emission under optical pumping has been obtained for a 2 nm BeCdSe/ZnSe multiple QWstructure at 80 K. The bowing parameter of the energy gap of this ternary alloy has been estimated as about 4.5 eV.

ZnOnanowires were mass produced using a physical vapor deposition approach. The ZnOnanowire monocrystallites have an average diameter around 60 nm and length up to a few micrometers. The unidirectional growth of the ZnOnanowires was controlled by the conventional vapor-liquid-solid mechanism. Intensive UV light emission peaked around 3.27 eV was observed at room temperature, which was assigned to emission from free exciton under low excitation intensity. The observed room temperature UV emission was ascribed to the decrease in structure defects as compared to bulk ZnOmaterials, and in particularly to the size effect in the ZnO wires.

We demonstrate the use of a amorphous starburst amine, 4, N-diphenyl- amino)triphenylamine (TDATA), doped with a very strong acceptor, tetrafluoro- tetracyano-quinodimethane by controlled coevaporation as an excellent hole injection material for organic light-emitting diodes(OLEDs). Multilayered OLEDs consisting of double hole transport layers of TDATA and triphenyl-diamine, and an emitting layer of pure 8-tris-hydroxyquinoline aluminum exhibit a very low operating voltage (3.4 V) for obtaining even for a comparatively large (110 nm) total hole transport layer thickness.

We demonstrate that the emission wavelength of quantum cascade lasers can be decreased significantly by incorporating InGaAs layers within the active regions. InAs monolayers are deposited during growth, with segregation effects resulting in the formation of thin InGaAs layers within the GaAs active region quantum wells of the laser. The InGaAs layers are positioned close to the antinodes of the lower laser level wave function, thus decreasing its confinement energy. The small spatial overlap of the InGaAs layers with the upper laser level minimizes the perturbation of the upper state. Consequently, the energy separation between the upper and lower laser levels increases, reducing the emission wavelength. The measured operating wavelength of is the shortest reported for a GaAs–AlGaAs quantum cascade laser and is approximately less than for an identical structure without InGaAs layers in the active regions.

We report record-low threshold current density and high output power for quantum cascade lasers operating up to 425 K. The threshold current density is 1.1, 3.83, and at 80, 300, and 425 K, respectively, for 5 μs pulses at a 200 Hz repetition rate. The cavity length is 3 mm with a stripe width of 20 μm. The maximum peak output power per facet is 1 W at 80 K, 0.5 W at 300 K, and more than 75 mW at 425 K. The characteristic temperature of these lasers is 174 K between 80 and 300 K and 218 K in the range of 300–425 K.

Microdischargedevices having inverted, square pyramidal cathodes as small as at the base and 35 μm in depth, have been fabricated in silicon and operated at gas pressures up to 1200 Torr. For the polyimide dielectric incorporated into these devices the discharges produced exhibit high differential resistance in Ne), ignition voltages for a single device of ∼260–290 V, and currents typically in the μA range. Arrays as large as have been fabricated. For an 8 μm thick polyimide dielectric layer, operating voltages as low as 200 V for a array have been measured for 700 Torr of Ne. Array lifetimes are presently limited to several hours by the thin (1200–2000 Å) Ni anode.

We report here experimental evidence of electron oscillation within the toroidal-section magnetic duct of a filtered vacuum arc plasma source. Our results clearly demonstrate that electrons can oscillate inside the duct under the combined effects of the electric and magnetic fields. In another experiment, we observe that, under the influence of the electron motion, the trajectories of the plasma ions are more or less unchanged except in the intensity when the Bilek plate is biased. Finally, our time-of-flight experiments show that the effects due to collisional scattering between plasma ions and oscillating electrons are masked by those associated with the metal plasma flow through the duct, and collisional scattering does not give rise to an increase of the mean charge state of the plasma ions. We conclude that the application of a bias voltage to the duct not only perturbs the ions but also influences the plasma electrons. Our results demonstrate that electrons at the central axis are one of the major reasons leading to improved plasma transport through the duct.

By introducing benzoyl–benzene into a cholesteric liquid crystal, the helix unwinding voltage was reduced. This reduction was roughly proportional to the concentration of the dopant and was present for driving frequencies across the audio spectrum. It is believed that this voltage reduction is primarily due to a perturbation of the intermolecular coupling in the liquid crystal mixture. It was found that so long as the long-range order was not destroyed, the helix unwinding voltage could be reduced by as much as 24% at 60 Hz.

Ordered ceramics are currently used as dielectricresonators for microwave and millimeter wave technologies. The degree of ordering is generally determined by x-ray techniques. In this work, we demonstrate that Raman spectroscopy can be used to evaluate the degree of long-range order of these materials. We also show how varying the degree of order of samples allows partial assignment of the optical vibrational modes.

Surface processes of the growingthin films of InAs on GaAs(001) substrates have been studied as a function of substrate temperature and As to In flux ratio. They have been observed by reflection high-energy electron diffraction and total-reflection-angle x-ray spectroscopy in real time. At temperatures lower than ∼480 °C, InAsgrows in a Stranski–Krastanov mode irrespective of the As/In flux ratio, while the growth mode of InAs strongly depends on the flux ratio above ∼500 °C. We have found that the sticking probability of In decreases as the As flux is decreased above ∼500 °C, which results in the changes in the growth mode of InAs.

Lattice-matched multiple-quantum-wellstructures were obtained on GaAs(001) using graded-composition layers to match the II–VI lattice parameter to the III–V substrate. Cross-sectional transmission electron microscopy studies show that the effect of the crosshatch pattern of the surface is limited to long-period coherent undulations of quantum well and barrier layers. Optical measurements of the excitonic properties as a function of well thickness, complemented by self-consistent calculations of the transition energies, indicate good quantum confinement in the well, with a 68% conduction band contribution to the 0.482 eV band gap difference.

Organic electroluminescent devices with a structure of ITO/ploy (9-vinylcarbazole)/tris (8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag are fabricated at different substrate temperatures (77, 298, and 438 K) during Alq3 deposition. It is found that the surface morphologies of Alq3 thin films greatly affect the characteristics of the devices by the contact area between metal cathode and light-emitting layer. There is an increase in the luminous efficiency of the devices in the order 77 K<298 K<438 K. We attribute this trend to different structures of Alq3 thin films.

The existence of "radiation-free" states in transient motion of dislocations is investigated. By analyzing an edge dislocation jumping from rest to a supersonic speed, we see that the Mach fronts disappear at because at this dislocation velocity, the pole singularity in the complex plane is replaced by a removable one. However, there exist radiated stress waves propagating with velocity as well as Also, due to radiated longitudinal waves, there is a “force” required to be supplied to sustain such a motion.

We apply the Krivoglaz theory of x-ray scattering to thin epitaxial films containing misfit dislocations and reanalyze the seemingly puzzling x-ray scattering phenomena observed in several heteroepitaxial films. We show that the two-line shape scattering distribution and its dependence upon film thickness and momentum transfer can be understood in natural way and on a quantitative level. Extended diffuse x-ray scattering maps have been obtained from which are discussed within the framework of this theory disclose a particular dislocation network at the interface.

Diamond samples grown by microwaveplasma chemical vapor deposition and doped with have been irradiated under thermal neutron flux of for 76 h to examine transmutation of to and the attendant lattice damage to diamond. To prevent graphitization and formation of diamond-like carbon, continuous cooling in water is provided during irradiation. Characterization of the diamond samples using Raman spectroscopy,photoluminescencespectroscopy, and secondary ion mass spectrometry showed that diamond remained crystalline without a major damage. Formation of vacancies due to neutron irradiation is inferred from photoluminescencespectroscopy.

The chemical interaction between the simple metals,aluminum and sodium, and crystalline copolymerthin films of vinylidene fluoride (70%) with trifluoroethylene (30%), has been studied using x-ray photoemission spectroscopy.Aluminum and sodium metalize the polymer differently and different binding sites for the two metals can be inferred from the corresponding core level shifts. Aluminum leads to enhanced screening of final photoemission states associated with the polymer, while sodiumdoping strongly influences the fluorine, but perturbs the carbon backbone only slightly.